In the human eye, the lens is embedded behind pupil and iris within a notch or recess of the vitreous body. The function of the lens is to adapt the eye from close vision to far vision and vice versa. For example, while reading a book, the eye has to be adjusted to a short distance. Contrary, while looking to an object in far distance, the lens has to perform a kind of “switching process”.
The lens is kept in its position by means of a kind of “suspension device”, the so-called zonules or suspensory ligaments, which emanate from the ciliary body. This ciliary body features the ciliary muscle, which is an annular muscle band. The ciliary muscle effectuates a stronger or weaker flection or curvature of the lens. When the ciliary muscle contracts, the zonules relax, such that the flection of the lens increases. Hence, the lens can become rounder with increasing contraction of the ciliary muscle, which increases the refraction power of the lens. This process is called “accommodation”. Contrary, when the ciliary muscle relaxes, the lens is straightened by the tension of the zonules.
Incident light rays are refracted variably by different bending states of the lens. The refractive power of the lens is changed. A larger flection of the lens results in a higher refraction of the light rays and a focusing for close vision is achieved. To adapt the lens for far vision, the process proceeds inversely. By alternating its refraction power, the lens enables close vision as well as far vision. The process of accommodation proceeds sort of “automatically”, since the ciliary muscle cannot be influenced deliberately.
The natural eye lens of the human starts loosing its elasticity approximately at the age of 40. The lens is not any more able to bend itself so strongly and it looses the aptitude to automatically focus on different distances (accommodation). For example, a 30 years old person is able to focus on a distance of 12 centimeters. In contrast to that, with an age of 40 focusing is possible on a distance of 20 centimeters and with an age of 50 on a distance of 60 centimeters. The loss of accommodability is also known as presbyopia.
The use of reading glasses is one possibility, to enable focusing on close distances. For example, a 60 years old person needs a correction of approximately plus three diopters for being able to focus on a 30 centimeters distance. For focusing on far distance, the glasses have to be removed.
Beyond that, so called bifocal glasses exist, the upper half of which is adapted for far vision and the lower half of which is adapted for close vision. However, the jump or break of vision in the middle of the glasses turns out to be distracting. In so called multifocal glasses these two zones merge continuously. However, also multifocal glasses turn out to be unsuitable for many spectacle wearers. Furthermore, contact lenses are known, which act like a multifocal glass on the eye. However, these lenses have the same drawbacks as the multifocal glasses.
Additionally, multifocal lenses are known, which are implanted as intraocular lenses replacing the natural eye lens. After removal of the body's own lens, intraocular lenses are inserted as implant into the empty capsular bag. The implant is an artificial lens consisting of several annuli with different refraction powers. The implant induces two focal points within the eye, one for far vision and one for close vision. On the distance in between, the patient's focus is not perfect.
Moreover, accommodating intraocular lenses are known. These potentially accommodating lenses concern lenses or lens systems, which are inserted instead of the natural lens after operative removal of the natural lens and which are mostly fixed within the capsular bag. Via a still existing, however, weak residual contractibility of the ciliary muscle and by means of a haptic an axial shift of the lens and thus, a shift of the focal point should be achieved.
The document DE 10 139 027 A1 describes an intraocular lens with preferably four radially outwards extending haptics. The haptics are connected articulately with the optic. By contraction of the ciliary muscle the lens is axially shifted forwards within the optical path by a deflector mechanism and thereby, the refraction power of the whole system is increased. Such implants allow for the reinstatement of an accommodation of approximately 1 dpt to 2 dpt.
This, however, is not sufficient, since for example for the ability to read, an accommodation of higher than 3 dpt has to be realized. Additionally, an exact positioning of the intraocular lens is difficult.